Warsaw, Poland
Warsaw, Poland
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Hirsch M.,Max Planck Institute for Plasma Physics (Greifswald) | Dinklage A.,Max Planck Institute for Plasma Physics (Greifswald) | Alonso A.,CIEMAT | Fuchert G.,Max Planck Institute for Plasma Physics (Greifswald) | And 62 more authors.
Nuclear Fusion | Year: 2017

Observations on confinement in the first experimental campaign on the optimized Stellarator Wendelstein 7-X are summarized. In this phase W7-X was equipped with five inboard limiters only and thus the discharge length restricted to avoid local overheating. Stationary plasmas are limited to low densities <2-3 • 1019 m-3. With the available 4.3 MW ECR Heating core T e ∼ 8 keV, T i ∼ 1-2 keV are achieved routinely resulting in energy confinement time τ E between 80 ms to 150 ms. For these conditions the plasmas show characteristics of core electron root confinement with peaked T e-profiles and positive E r up to about half of the minor radius. Profiles and plasma currents respond to on- and off-axis heating and co- and counter ECCD respectively. © 2017 Max-Planck-Institut fuer Plasmaphysik.

Lerche E.,Laboratory for Plasma Physics Brusells | Lerche E.,Culham Center for Fusion Energy | Goniche M.,French Atomic Energy Commission | Jacquet P.,Culham Center for Fusion Energy | And 21 more authors.
AIP Conference Proceedings | Year: 2015

Ion cyclotron resonance frequency (ICRF) heating has been an essential component in the development of high power H-mode scenarios in JET-ILW. The steps that were taken for the successful use of ICRF heating in terms of enhancing the power capabilities and optimizing the heating performance in view of core impurity mitigation in these experiments will be reviewed.

Goniche M.,French Atomic Energy Commission | Dumont R.J.,French Atomic Energy Commission | Bobkov V.,Max Planck Institute for Plasma Physics (Garching) | Buratti P.,ENEA | And 25 more authors.
Plasma Physics and Controlled Fusion | Year: 2017

Ion cyclotron resonance heating (ICRH) in the hydrogen minority scheme provides central ion heating and acts favorably on the core tungsten transport. Full wave modeling shows that, at medium power level (4 MW), after collisional redistribution, the ratio of power transferred to the ions and the electrons vary little with the minority (hydrogen) concentration n H/n e but the high-Z impurity screening provided by the fast ions temperature increases with the concentration. The power radiated by tungsten in the core of the JET discharges has been analyzed on a large database covering the 2013-2014 campaign. In the baseline scenario with moderate plasma current (I p = 2.5 MA) ICRH modifies efficiently tungsten transport to avoid its accumulation in the plasma centre and, when the ICRH power is increased, the tungsten radiation peaking evolves as predicted by the neo-classical theory. At higher current (3-4 MA), tungsten accumulation can be only avoided with 5 MW of ICRH power with high gas injection rate. For discharges in the hybrid scenario, the strong initial peaking of the density leads to strong tungsten accumulation. When this initial density peaking is slightly reduced, with an ICRH power in excess of 4 MW,very low tungsten concentration in the core (∼10-5) is maintained for 3 s. MHD activity plays a key role in tungsten transport and modulation of the tungsten radiation during a sawtooth cycle is correlated to the fishbone activity triggered by the fast ion pressure gradient. © 2017 IOP Publishing Ltd.

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